1. Field of the Invention
The present invention relates to an exposure device and an image forming apparatus suitable for an electrophotographic apparatus.
2. Description of Related Art
FIG. 9 of the accompanying drawings schematically shows a side elevational view of an LED (light emitting diode) printer. An LED printer 14xe2x80x2 is equipped with a paper cassette 15, four printing units 17xe2x80x2, a conveying belt 18, a fixing unit 19, and an outlet port 20.
The LED printer 14xe2x80x2 prints a color image on paper 16 using toners of four colors, yellow, magenta, cyan and black, and includes four printing units 17xe2x80x2, which are substantially identical in construction, one for each of the four colors, and are arranged in series along the travelling path of the paper 16.
The photosensitive drum 2 of the individual printing unit 17xe2x80x2 is disposed so as to extend perpendicularly across the traveling path of the paper 16. The charging unit 26, the exposure unit 27xe2x80x2, the developing unit 28, the transferring unit 29, the discharging unit 30 and the cleaning unit 31 are arranged on and around the circumference of the photosensitive drum 2 for performing the respective functions while the photosensitive drum 2 makes a single rotation.
The paper cassette 15 holds the paper 16, which is not printed yet, to supply and deliver it to the printing units 17xe2x80x2 as a demand arises, and the conveying belt 18 conveys the paper 16 to the individual printing units 17xe2x80x2.
The fixing unit 19 fixes a toner image formed in the printing units 17xe2x80x2, and the outlet port 20 allows the paper 16, which has been printed in color, to be removed out of the LED printer 14xe2x80x2.
Color-printing is performed on the LED printer 14xe2x80x2 in the following manner. The paper cassette 15 delivers one sheet of the paper 16 at a time onto the conveying belt 18. The conveying belt 18 then brings the paper 16 to the printing units 17xe2x80x2 where the individual printing units 17xe2x80x2 sequentially form toner images of colors of yellow, magenta, cyan and black.
In the individual printing unit 17xe2x80x2, the charging unit 26 electrically charges the circumferential surface of the photosensitive drum 2 uniformly. Then the exposure unit 27xe2x80x2 forms an electrostatic latent image on the circumferential surface of the photosensitive drum 2 in accordance with an original image to be printed. Then the developing unit 28 develops the latent image with toner, bringing the latent image into a visible image of the toner. After that, the transferring unit 29 transfers the toner of the visible image to the paper 16, at which time the toner image on the paper 16 is not fixed yet.
After the toner image is transferred to the paper 16, the discharging unit 30 discharges the circumferential surface of the photosensitive drum 2, whereupon the cleaning unit 31 removes residual toner.
Subsequently in the first printing unit 17xe2x80x2, the paper 16 to which toner image of the first primary color (yellow) transferred by the transferring unit 29 is conveyed to the second printing unit 17xe2x80x2 on the conveying belt 18. Then in the second printing unit 17xe2x80x2, third and fourth printing units 17xe2x80x2, toner image in the same printing process as in the first printing unit 17xe2x80x2 is performed. Likewise, as a result, in each of the toner images of the other colors (magenta, cyan and black) are formed on the same paper 16.
The paper 16, with the color toner image formed on it by the four printing units 17xe2x80x2, is transferred to the fixing unit 19 by the conveying belt 18 to be fixed and then is removed out of the LED printer via the outlet port 20 as color-printed paper.
FIG. 10 schematically shows a cross-sectional view of an exposure device which is applied to the LED printer of the related art. An exposure device 1xe2x80x2 of FIG. 10 is installed in the exposure unit 27xe2x80x2 (FIG. 9) and has an exposure body 124 and an image forming lens 109. The exposure body 124 is composed of an outer casing 122 and an inner casing 123, which are generally C-shaped in cross section, the inner casing 123 being telescopically fitted in the outer casing 122 with their through-hole side facing each other to define a light-emitting space 121 inside the exposure body 124.
On the bottom wall of the light-emitting space 121 (hereinafter called the light-emitting-space bottom wall 134), a print board 112 is disposed on which a plurality of sets of light emitting diode microchips (hereinafter called the LED microchips 104) and driver elements 105 are arranged in array in series perpendicularly to the drawing sheet of FIG. 10.
The LED microchips 104 is circuits on which a plurality of light emitting diodes are mounted, and the driver elements 105 are driver circuits to energize the associated LED array 103. The LED microchip 104 and the driver element 105 of each set are electrically interconnected via an upwardly arcuate wires 106. Each light emitting diode of the LED microchip 104 is connected to a corresponding driver element 105.
The wires 106 connect the LED microchips 104 and the driver elements 105 with or without a wire ball. The wire-ball-free connection is technically more difficult than the with-wire-ball connection.
A through-hole 125 is disposed above the LED microchip 104 in the light emitting space 121, in which an image forming lens 109 is mounted in such a posture that the center line 109A of the image forming lens 109 coincides with the center of beam intensity distribution outputs (hereinafter called the intensity-distribution-center line 107) of the LED microchip 4.
The rotation center 2A of the photosensitive drum 2 is disposed on the upward extension of the center line 109A of the image forming lens 109. The beam output from the LED array 103, through the image forming lens 109, strikes the circumference of the photosensitive drum 2 to form a latent image on it.
However, in the exposure device 1xe2x80x2, a local beam emitted from the LED array 103 reflects on the wires 106 (hereinafter, the beam reflects on the wire 106 is called the stray light 110), which connect the LED microchips 104 and the driver elements 105, and then tends to enter the image forming lens 109 since the beam-intensity-distribution center line 107 coincides with the center line 109A of the image forming lens 109.
The stray light 110, as well as local part of the beam directly strikes the incidence surface 109B of the image forming lens 109 output from the LED array 103 (hereinafter called the proper beam 108), strikes the incidence surface 109B of the image forming lens 109. As a result, the stray light 110 forms an undesired latent image on the circumferential surface of the photosensitive drum 2 and becomes one cause for deterioration of the quality of a printed image.
With the foregoing problems in view, it is an object of the present invention to provide an exposure device and an image forming apparatus in which a more vivid printed image can be formed as possible stray light is prevented from the striking image supporting body.
According to a first concept of the present invention, there is provided an exposure device comprising: a driver element; a light emitting diode microchip connected to the driver element by wires and having a light emitting diode array for outputting light for exposure; and an image forming lens for directing the light output from the light emitting diode array of the light emitting microchip onto an image supporting body as exposure light; the image forming lens being disposed in such a posture that the center line of the image forming lens is out of axial alignment with the center line of intensity distribution of the light output from the light emitting diode array on an incidence surface of the image forming lens so as to reduce possible incidence of stray light when local part of the light output from the light emitting diode array reflects on the wires.
As a preferable feature of the first concept, the image forming lens may be disposed off the center line of intensity distribution of the light output of the light emitting diode array.
As another preferable feature, the image forming lens may extend parallel to the center line of intensity of distribution of the light output of the light emitting diode array, or be inclined with respect to the center line of intensity distribution of the light output of the light emitting diode array.
According to a second concept of the present invention, there is provided an exposure device comprising: a driver element; a light emitting diode microchip connected to the driver element by wires and having a light emitting diode array for outputting light for exposure; and an image forming lens for directing the light output from the light emitting diode array of the light emitting diode microchip onto an image supporting body as exposure light; the image forming lens being disposed in such an inclined posture that a first imaginary plane perpendicular to an incidence surface of the image forming lens crosses a second imaginary plane perpendicular to a light emitting surface of the light emitting diode array on the light emitting surface of the light emitting diode array so as to reduce possible incidence of stray light when local part of the light output from the light emitting diode array reflects on the wires.
As a preferable feature of the second concept, the center line of the image forming lens may be disposed, toward a wire-free side of the light emitting diode microchip, off the center line of intensity distribution of the light output of the light emitting diode array.
As another feature, the individual wire connecting between the light emitting diode microchip and the driver element has a wire ball at at least one end, the center line of the image forming lens being disposed, toward a wire-ball side of the light emitting diode microchip, off the center line of intensity distribution of the light output of the light emitting diode array.
According to a third concept of the present invention, there is provided an image forming machine comprising: an image supporting body to be charged with electricity; an exposure device for exposing the image supporting body, which is charged with electricity, to light to form a latent image on the image supporting body in terms of a pattern of areas left undischarged; a developing unit for applying a developer to the image supporting body, which is charged with electricity and is exposed to the light by the exposure device, so that the developer adheres only to the undischarged areas to bring the latent image into a visible image of the developer; and a transferring unit for transferring the developer of the visible image from the image supporting body onto a medium; the exposure device including: a driver element, a light emitting diode microchip connected to the driver element by wires and having a light emitting diode array for outputting light for exposure, and an image forming lens for directing the light output from the light emitting element array of the light emitting microchip onto the image supporting body as exposure light, the image forming lens being disposed in such a posture that the center line of the image forming lens is out of axial alignment with the center line of intensity distribution of the light output from the light emitting array on an incidence surface of the image forming lens so as to reduce possible incidence of stray light when local part of the light output from the light emitting diode array reflects on the wires.
According to a fourth concept of the present invention, there is provided an image forming machine comprising: an image supporting body to be charged with electricity; an exposure device for exposing the image supporting body, which is charged with electricity, to light to form a latent image on the image supporting body in terms of a pattern of areas left undischarged; a developing unit for applying a developer to the image supporting body, which is charged with electricity and is exposed to the light by the exposure device, so that the developer adheres only to the undischarged areas to bring the latent image into a visible image of the developer; and a transferring unit for transferring the developer of the visible image from the image supporting body onto a medium; the exposure device including: a driver element; a light emitting diode microchip connected to the driver element by wires and having a light emitting diode array for outputting light for exposure, and an image forming lens for directing the light output from the light emitting element array of the light emitting microchip onto the image supporting body as exposure light, the image forming lens being disposed in such an inclined posture that a first imaginary plane perpendicular to an incidence surface of the image forming lens crosses a second plane perpendicular to a light emitting surface of the light emitting diode array on the light emitting surface of the light emitting diode array so as to reduce possible incidence of stray light when local part of the light output from the light emitting diode array reflects on the wires.
Accordingly, in the exposure device and the image forming apparatus of the present invention, the center line of the image forming lens is out of axial alignment with the center line of intensity distribution of the light output from the light emitting diode array on an incidence surface of the image forming lens so as to reduce possible incidence of stray light when local part of the light output from the light emitting diode array reflects on the wires. As an advantageous result, the quality of printed image is improved.
Further, the center line of the image forming lens can be inclined with respect to the center line of intensity distribution of the light output of the light emitting diode array. As another advantageous result, more amount of beam enters the image forming lens 9 and the exposure light is uprated.
The image forming lens can be disposed in such an inclined posture that a first imaginary plane perpendicular to an incidence surface of the image forming lens crosses a second imaginary plane perpendicular to a light-emitting surface of the light emitting diode array on the light-emitting surface of the light emitting diode array so as to reduce possible incidence of stray light when local part of the light output from the light emitting diode array reflects on the wires. As still another advantageous result, the exposure light is uprated since an increased amount of exposure light enters the incidence surface of the image forming lens, and an more vivid image is created since the exposure light output from light emitting diode array enters the image forming lens parallel to the center line of image forming lens preventing the exposure light from deteriorating.